1. Field of the Invention
The invention relates to a thermostatic element of the type comprising a cap an elongated shape, and which contains a material substantially expandable and contractible as a function of the direction of variation of its temperature. A piston moveable relative to the cap in the longitudinal direction of the cap is coupled to the expandable and contractible material so as to be displaced in opposite directions, depending on whether the material expands or contracts.
Such thermostatic elements are used, in particular, in the field of setting the temperature of a fluid obtained from the mixture of two fluid streams at different temperatures. The relative movement of the piston and cap is employed in order to change the proportion of the mixture of the two fluid streams.
For a large number of applications in this field, it is necessary for the response of the thermostatic element to be very fast. In other words, the change in the temperature of the medium in which the cap is located gives rise in a very short time to a corresponding movement of the piston. This is particularly true of thermostatic elements immersed in a stream of water feeding a sanitary installation, in which application, when an ideal temperature has been selected, a fall in temperature of three of only four degrees is very unpleasant and an increase of a few degrees may cause burns.
2. Description of the Prior Art
The thermostatic elements used conventionally in this type of application comprise, for example, according to FIGS. 1 and 2, a metallic cap 1 possessing a part 11 which has a cylindrical general shape of circular cross section and a bottom end 12 which is closed. The opposite end of cap 1 widens and is connected to a collar 13, and a sleeve 2 having a shape of revolution with a central duct 21 and a base 22 is accommodated in the collar of the cap in such a way that, with the exception of the base 22, the sleeve 2 extends out of the cap in the opposite direction to the cylindrical part 11 of the cap so as to be coaxial with the cap. The collar 13 is crimped around the base 22.
The cylindrical part 11 of the cap is filled with a mass of material, such as wax mass 3, which is highly expandable and contractible as a function of the variations in temperature, particularly variations around the usual ambient temperature. The base 22 of the sleeve comprises, in its face confronting this wax mass, an annular receptacle 23 in which is anchored the periphery of a disk-shaped and elastically deformable diaphragm 4 shutting off the central duct 21 of the sleeve on the same side as the cap 1. Inside the duct 21 of the sleeve is accommodated a piston 5 subjected to the movements of the central region of the diaphragm. The end of this piston which is opposite the diaphragm projecting out of the sleeve to a greater or lesser extent as a function of the volume occupied by the wax and, therefore, as a function of the temperature of the wax. A protective tubular part hood or concertina 6 surrounds part of the sleeve 2 and part of the piston 5, the ends of the hood or concertina being immobilized in grooves 24, 51 made in the perimeter of these two components. This hood or concertina 6, in the form of a flexible unwinding or rolling membrane, follows the movements of the piston without any elastic deformation. The piston 5 is subjected to the movements of the central region of the diaphragm 4 by a plug 7 made of deformable elastomer, in contact against that surface of the diaphragm which is opposite the wax mass, and by of a washer 8 made of polymer, such as PTFE, inserted between the plug and the piston and fitted into the duct 21 in order to prevent the elastomer of the plug from creeping around the piston.
For the purpose of fixing the thermostatic element in a thermostat, its sleeve 2 has a threaded region 25, designed for receiving, for example, a nut, and a shoulder 26 such that a supporting piece can be gripped between the shoulder and the nut, if appropriate, with a nut locking device being interposed.
The general design of these thermoplastic elements is highly suited to the use of a wax, the coefficient of expansion of which is very high in relation to that of common fluids (about 10 to 20 times higher) and is therefore capable of causing a very pronounced movement of the piston. Unfortunately, these waxes have very low thermal conductivity (about 1000 times lower than that of copper), and therefore the temperature of the wax mass as a whole reflects only inadequately, and with a long delay, the temperature of the fluid in which the cap is immersed. For this reason, the wax is usually xe2x80x9cloadedxe2x80x9d with a powder consisting of a material having high thermal conductivity, for example a copper powder of suitable grain size. For the sake of simplification, xe2x80x9cwaxxe2x80x9d will designate hereafter both loaded materials and nonloaded materials and also single-component waxes. However, all these expedients are insufficient for obtaining a fast-response thermostatic element capable of being used without any special precaution in a sanitary installation.
The object of the invention is to overcome this disadvantage and to provide a fast-response thermostatic element, the manufacture of which is simple and not appreciably more complicated than that of the known thermostatic elements and which has a high degree of reliability.
To achieve this, the invention relates to a thermostatic element of the type comprising a cap having an elongated shape, containing a displacement material substantially expandable and contractible as a function of the direction of variation of its temperature. A piston moveable relative to the cap in the longitudinal direction of the cap is coupled to the expandable and contractible material so as to be displaced in opposite directions, depending on whether the material expands or contracts. The thermostatic element is defined in that the side wall of the cap has flats or depressions (dents) around the cap which extend in the longitudinal direction of the cap and which delimit an inner space. The cross section of the cap, over which the flats or depressions extend, has a lobed shape, and an insert accommodated and fixed in the cap extends in the longitudinal direction of the cap.
Due to the fact that the side wall of the cap of the thermostatic element comprises dents such as flats or depressions resulting in lobes, as seen in cross section, the entire inner space of the cap is close to a plurality of regions of the side wall, with the exception of the central region of the cap. However, due to a suitable positioning of the insert in the cap, the quantity of wax or the like contained in this central region may be small and the greatest part of this material may be located in the lobes, thus allowing the variations in temperature of the medium outside the thermostatic element to be transmitted quickly to the entire mass of material contained in the cap. Moreover, the total quantity of material having low thermal conductivity is substantially smaller.
The thermostatic element according to the invention may, furthermore, have one or more of the following characteristics. The insert may consist of a material of high thermal conductivity. The insert may consist of a material of markedly lower thermal conductivity than that of the expandable and contractible material. The side wall of the cap may have three flats or depressions delimiting a cap inner space, the cross section of which has three lobes. The side wall of the cap may have two flats or depressions delimiting a cap inner space, the cross section of which has two lobes extending in opposite directions. The side wall of the cap may have more than three flats or depressions delimiting a cap inner space, the cross section of which has more than three lobes. The insert may have a cylindrical general shape, may consist of a plate, may consist of a folded plate comprising two parallel tabs, may have one end provided with fins, and may be welded to the side wall of the cap. The cap may comprise a bottom region having cavities. The insert may be welded to a washer, itself welded to the cap, or may comprise fins accommodated in cavities of the cap.